I had huge fun writing the story about whale poo which is out in Current Biology today. According to recent research, the net effect of sperm whales is that they help to remove carbon dioxide from the atmosphere. They do this by picking up iron rich food in the deep, and defecating most of the iron near the surface. This encourages the growth of (iron-limited) diatoms, which after their death sink to the sea floor and take their carbon with them.
Which means, of course, that reducing sperm whale populations by 90 % in the era of industrial whaling may well have had a significant effect on greenhouse gas concentrations.
Current Biology, Volume 20, Issue 13, R541, 13 July 2010
summary and limited access to pdf file